(1) Field of the Invention
The present invention relates to a multi-wire saw used for cutting a workpiece into slices or wafers, in particular relating to a wire-guide structure used in a multi-wire saw.
(2) Description of the Prior Art
A multi-wire saw is one of the cutting machines used for cutting a workpiece such as a silicon ingot, crystal, quartz, etc., having a cylindrical or block shape, into wafers, and is known to cut a workpiece being abutted against the lines of the wire which are arranged in parallel bearing abrasive grain thereon and are traveling at a high speed, into a multiple number of wafers. The multi-wire saw of this type has a configuration as schematically shown in FIG.1, and comprises feeding and collecting spools 22 and 23 for feeding and taking up wire 21, three wire guides 24 which have a cylindrical exterior configuration and are arranged in parallel to each other, and feeder and collector pulleys 25 and 26 disposed between spools 22, 23 and the wire guide 24 in the upper portion. In FIG.1, three wire guides 24 are used, but there are multi-wire saws which have two or four wire guides, as is well known.
Each wire guide 24 used in the multi-wire saw has a peripheral surface having a multiple number of circumferentially extending wire guiding grooves 27 formed thereon in parallel to each other at regular intervals along the axial direction of wire guide 24. Wire 21 fed from feeding spool 22 by way of feeder pulley 25 is tensioned across wire guides 24 whilst the wire is wound around each of the wire guiding grooves of wire guides 24 in turn, and is taken up by way of collector pulley 26 by collecting spool 23. The peripheral surface of each wire guide 24 is covered with a coating material 28 of urethane.
Lines of wire 21 arranged in parallel which are tensioned between a pair of wire guides 24 located in the lower portion of the multi-wire saw and are traveling at a high speed, are supplied drop-wise with an abrasive grain liquid from an abrasive grain liquid supplying nozzle 29. A workpiece 30 is pressed against the lines of wire 21 bearing the abrasive grain thereon. Therefore, workpiece 30 which is being pressed against the lines of wire 21 will be sliced into a multiple number of wafers having a thicknesses corresponding to respective spacing distances between successive lines of wire 21. The spacing interval between these lines of wire 21, or the spacing pitch between wire guiding grooves 27 on each wire guide 24 may be previously adjusted so that a multiple number of sliced pieces of workpiece 30 having a prescribed thickness can be obtained.
The conventional multi-wire saws thus configurated have suffered from the following drawbacks. First, a wire guide 24 which itself weighs about 60 Kg needs to be formed, on its peripheral surface, i.e., coating surface 28 with a multiple number of parallel wire guiding grooves 27. The job of machining the grooves needs much time and labor so is costly.
Further, since wire 21 runs at a high speed within wire guiding grooves 27 formed on the peripheral surface of wire guides 24, this unavoidably wears out wire guiding grooves 27 or damages them. With such damage, the spacing distance between the neighboring wire guiding grooves 27 changes, resulting in difficulty in maintaining cutting accuracy of workpiece 30. Moreover, when the cutting precision of workpiece 30 lowers, wire guides 24, which are heavy, should be replaced. This replacing task also needs much time and labor increasing the cost.